The present invention relates to the field of turbomachines, and more particularly it relates to the interface between the high pressure turbine and the combustion chamber in turbojets that are fitted with a combustion chamber made of ceramic matrix composite (CMC).
Conventionally, in a turbomachine, the high pressure turbine (HPT) and in particular its inlet nozzle, the combustion chamber, and the casing (or shell) of said chamber are all made of the same material, generally of the metal type. However, under certain particular conditions of use, implementing very high temperatures, a combustion chamber made of metal can be completely unsuitable from a thermal point of view and it is necessary to use a chamber made of high temperature composites of the CMC type. Nevertheless, the difficulties of working such materials and the expense thereof mean that use of such materials is usually limited to the combustion chamber itself, with the high pressure turbine inlet nozzle and the casing then continuing to be made more conventionally out of metal materials. Unfortunately, metal materials and composite materials have coefficients of thermal expansion that are very different. This gives rise to particularly severe interface problems with the nozzle at the inlet of the high pressure turbine and connection problems with the casing of the chamber.
The present invention mitigates these drawbacks by proposing a casing-chamber connection having the ability to absorb the displacements caused by the differences between the expansion coefficients of those parts. An object of the invention is thus to propose a structure of simple shape that is particularly easy to manufacture.
These objects are achieved by a turbomachine comprising a shell of metal material containing along a gas flow direction F: a fuel injection assembly, a combustion chamber of composite material, and a nozzle of metal material forming the fixed-blade inlet stage of a high pressure turbine, said nozzle being supported by said shell and being fixed thereto by first releasable fixing means, wherein said combustion chamber is mounted in floating manner inside said shell and is held in position solely by said nozzle to which it is fixed in resilient manner by second releasable fixing means.
By this direct connection (integration) of the combustion chamber and the nozzle, without any connection with the shell, manufacture of said chamber is considerably simplified, while simultaneously greatly improving sealing between the chamber and the nozzle. In addition, the resulting good alignment of the gas stream in operation enables the high pressure turbine to be fed more effectively. Eliminating the usual flanges of the combustion chamber (for connection to the shell) also achieves an appreciable saving in weight for said chamber and thus for the turbomachine.
By integrating the nozzle with the chamber, problems of relative displacement between the chamber and the shell are transferred to the nozzle, and provision is made for the first releasable fixing means to be adapted to enable said nozzle to expand freely in a radial direction relative to the shell.
In a preferred embodiment, said second releasable fixing means comprise firstly first holding means for holding an inner axially-extending wall at the end of said combustion chamber clamped between an inner circular platform of the nozzle and a flange serving to support an inner annular wall of said shell, and second holding means for holding an outer axially-extending wall at the end of said combustion chamber with resilient prestress against an outer circular platform of the nozzle.
Preferably, said support flange is subdivided into sectors to compensate for circumferential geometrical differences that result from the differential expansions that exist at high temperatures between said inner circular platform of the nozzle and said inner axially-extending wall of the combustion chamber. Said support flange is mounted between a flange of said inner annular wall of the shell and a ring of metal material held against said flange by said first releasable fixing means.
Advantageously, said first releasable fixing means comprise a plurality of bolts with the screw shanks thereof that pass through respective corresponding oblong holes of said support flange being provided with respective shoulders against which said ring is caused to bear so as to enable said support flange to slide between said ring and said flange of the inner annular wall of the shell.
In order to provide sealing for the turbomachine, said flange of the inner annular wall of the shell has a circular groove for receiving an omega type circular sealing gasket for providing sealing between said flange of the inner annular wall of the shell and said support flange. Likewise, a composite material ring advantageously brazed on said outer end wall of the combustion chamber is held with resilient prestress against said outer circular platform of the nozzle by the second holding means, said ring having a circular groove for receiving a circular sealing gasket of the omega type for providing sealing between said outer end wall of the combustion chamber and said circular outer platform of the nozzle.